It has probably been at least 10 years since you have been able to do anything to improve the soil. I would take it all out and work compost into the soil before replanting. Al

yes, I think you are correct. I've only been in the house a year. The gazania could be as much as 10-15 years old. There is an area about 24" accross were some kind of black decay occurred and the trailing gazanias completely died in the area. Now it's starting to happen in another area. I think I should just pull it all out and replant.